Color photography



Patented Nov.*30,*1937 coLoR PHO Gerd Heymer, Dessau-in signor to Agfa Ansco 1 ton, N. Y., a corporati TOGRAPHY -Anhalt, Germany, as-

Corporation, Bingham -v on of New York I No Drawing. Application October 21, 1933, Se-

rial No. 694,68

9. In Great Britain May 5, 1932 6 Claims. (CI. 9588) My present invention relates to color photography. It is a continuation-in-part of my application Ser. No. 646,703, filed Dec. 10, 1932.

One of its objects is to provide a process for the conversion of pictures having a silver image (herein referred'to as silver pictures) into picturesliaving an image in color (herein referred to as jfcolor pictures"). Another object is the .bath used for the conversion of the silver picture 10 into the dyestufi' picture. Further objects will be seen from the detailed specification following hereafter. I v It is based on the observation that the amdyestuffs which are liable to reduction by an aqueous solution of sodium hydrosulfite have proved particularly suitable for the conversion of silver pictures into color pictures. However, not all of these dyestuffs yield good results, but essentially those of which the reaction products, formed after the treatment with a solution of sodium hydrosulfite, are soluble in water or aqueous solutions and do'not quickly regenerate the dyestufi under the influence of oxygen. The photographic material is dyed with the azo-dyestun according to known methods. As dyestufis which are suitable for carrying out this invention there may be named, for instance, Congo Pure Blue (Schultz, Farbstofiftabellen 1931, vol. 1, A. 513'), Sirius Red-Violet R (cf. Schultz, Farbstofitabellen 7th Edn., vol. 2, page 198, lines 19-23), Sirius Ruby B (cf. Schultz, Farbstofftabellen, 7th Edn., vol. 2, page 198, lines 24-26), Benzo-Light Yellow (cf. Fierz-David Kiinstliche organische Farbstofi'e, 1926, page 168), Chrysophenin G or W (Schultz, Farbstofitabellen,'1923, 6th Edition No. 304) and Brilliant Benzo-Fast- Green (obtainable-by diazotizing the azo-dyestuff from diazotized 2-naphthylamino-8-sulfonic acid and 1-amino-2-naphthol ethyl ether with sodium nitrite and hydrochloric acid, isolating the intermediate product formed and adding it in admixture with water to a solution of l-acetylamino-8-naphthol-3:G-disulfonic acid which has been made alkaline by addition of sodium bicarbonate and to which pyridine has been added).

According to this invention, the layer dyed with a dyestufi of the kind above defined is subjected to the action of a reducing solution which contains a reducing agent whose reducing action is such that it does not reduce the dyestufi when used alone. Apparently the reducing agent is activated catalytically by the metallic silver, whereby the metallic silver is partially converted into an insoluble salt, that is to say, the metallic silver is oxidized. For instance, hydriodic acid compound.

. fore, there should be present in the reducing bath an agent which is adapted to form a complex compound with the silver of the silver picture. In this case, the complex silver compound acts as a catalyst and by this action the reduction of the dyestufi occurs with the solution of a reducing agent which would not reduce the dyestufi' without the formation of the silver complex The following example illustrates the inven tion:

For the production of a red picture a positive is copied on to a photographic material provided with a light-sensitive silver halide emulsion layer dyed with Benzo Light-Red 8 BL (Schultz, Farbstofitabellen 1931, 6th Edition, No. 566). The dyestuff can be applied by bathing the 'photographic material in an aqueous solution of the 30 dyestufi or in any other known manner. The exposed material is then developed, fixed in the usual manner and then treated in a bath obtained by mixing equal parts of Solution I 85 Water or 6250 Iodine grams 17 Potassium iodide do 33 Concentrated sulfuric acid cc 525 40 I and Solution II Water or 6250 Sodium sulfite grams 330 45 Thiourea do 330.

This solution has the property of destroying the dyestufi at the places where the silver is deposited, and removing most of the silver, whilst it does not afiect the unchanged silver bromide. Any silver which may remain after the bleaching operation is removed by treatment with an acidified solution of copper chloride, followed by a fixing operation. On account of this fixing operation, the fixing operation following the develop sible to produce color colored photographic Thefinished picture is a red positive. The photographic layer is preferably subjected to an intensive tanning operation.

The process of the invention is applicable not only to the production of a single color picture but for all purposes of color photography where layers are used; for instance, several difierently colored photographic layers can be treated simultaneously. It is pospictures by the treatment of exposed photographic layers which have been dyed before exposure to light, as well as to dye a silver picture and to treat it as described in the foregoing example, whilst omitting veloping and fixing operation.

What .I claim is: 1. A solution for discharging dye in the presence of silver and dissolving a silver image in color photography'which comprises equal parts of Solution I water cc. 6250 Io e rams" 17 Potassium iodide grams 33 Concentrated sulfuricv acid cc. 525 and solution II Water cc. 6250 Sodium .sulflte grams 330 Thiourea. grams 330 2. A photographic process of producing a color picture which comprises copying a positive onto a photographic material provided with a sensitized silver halide emulsion layer dyed with Benzo-Light Red 8 BL, treating said exposed emulsion layer in a bath obtained by mixing equal parts of 5 treating the picture with an acidified solution of g 9,106,594. ment, as hereinbetore described, can'beomitted.

the first decopper chloride and subjecting the treated material to a fixing operation.

3. A process of producing a color picture which comprises copying a positive onto a photographic material provided with a sensitized silver halide emulsion layer dyed with an azo-dyestuff which is capable of being reduced to compounds which are water soluble and do not quickly regenerate the dyestuff under the influence of oxygen, treating the exposed emulsion layer with a'solution containing a compound selected from the group consisting of hydrobromic and hydroiodic acid which is capable of reducing the dye in the presence of si1ver,-a compound capable of forming a complex silver salt with the sliver of the silver picture,.and an acid, and subjecting the treated material to a fixing operation.

4. A process of producing a color picture which comprises copying a positive onto a photographic material provided with a sensitized silver halide emulsion layer dyed with an azo-dyestufi which is capable of being reduced to compounds which are water soluble and do not quickly regenerate the dyestufl' under the influence of oxygen, tr'eating the exposed emulsion layer with a solution containing a compound selected from the group consisting of hydrobromic and hydroiodic acid which is capable of reducing the dye in the presence of silver, a thiourea capable of forming a complex silver salt with the silver of the silver picture, and an acid, and subjecting the treated material to a fixing operation.

5. A solution for discharging dye in the presence of silver and dissolving a silver image, in color photography comprising a compound selected from the group consisting of hydrobromic and hydroiodic acid capable of reducing azodyestuffs in the presence of metallic silver, an agent capable of forming with the silver of the silver picture a complex silver salt, and an acid.

6. A solution for discharging dye in the presence of silver and dissolving a silver image, in color photographycomprising a compound selected from the group consisting of hydrobromic and hydroiodic acid capable of reducing azodyestufl's in the presence of metallic silver, a thiourea capable of forming with the silver of the silver picture a complex silver salt, and an 

